If you have/get the equipment and willing to develop the skill, all paint is "temporary". But for $200-400, Plasti-Dip is pretty much the way to go.
It goes on over any surface, really. Anyone who says it "won't work" over fiberglass is full of crap.
There's a few cars on this forum who have Plasti-Dip finishes; I remember reading it in their build thread.
https://www.dipyourcar.com/collections/popular-car-kits
All the basic colors are there; you can give it a top coat if you like the paint shiny, otherwise it will look a lot like a Cobra race car would've back in the day. And provided you put the coats on heavy enough (5 wet coats, minimum) it should all peel off when you're done with it. If it won't peel, shoot a couple more coats on it, until it will.